Conventionally, as one of methods for fixing permanent magnets to a laminated rotor core used in a motor, a method of fixing permanent magnets with resin material has been proposed. Such a method is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2002-34187, comprising the steps of: placing a laminated rotor core in a resin sealing apparatus (also referred to as resin filling apparatus) having upper and lower dies, the laminated rotor core being formed by stacking a plurality of core pieces and having a plurality of magnet insertion holes for insertion of permanent magnets around a central axial hole; supplying liquid resin material from resin reservoir pots formed in the upper die into the magnet insertion holes respectively having the permanent magnets therein; and heating the laminated rotor core to thermally cure the resin material.
The laminated rotor core is formed by a stack of core pieces blanked out from an electromagnetic steel sheet. Therefore, the temperature of the resin material is reduced when the resin material melted by heating is filled into the magnet insertion holes, which disadvantageously reduces fluidity of the resin material. Accordingly, the conventional method has difficulty in filling the resin material into the magnet insertion holes and also in curing the resin material filled in the magnet insertion holes.
To overcome the problems, the laminated rotor core is disposed in the resin sealing apparatus having the upper and lower dies and is heated to a melting temperature of the resin material by heaters incorporated in the upper and lower dies. Subsequently, the liquid resin material having a favorable fluidity is supplied into the magnet insertion holes and is cured. This countermeasure allows the permanent magnets inserted in the magnet insertion holes to be retained firmly by the resin material.
However, since the melting temperature of the resin material (e.g., an epoxy resin) is as high as around 170° C., for example, it takes several dozens of minutes for the laminated rotor core to reach the melting temperature of the resin material. Until the core reaches the melting temperature, filling of the resin material into the magnet insertion holes must be waited. Accordingly, filling operation of the resin material is greatly affected by preheating operation of the core by the heaters of the upper and lower dies, which greatly reduces operating efficiency of filling of the resin material (productivity of the resin sealing apparatus).
The present invention has been made to overcome the above disadvantages of the prior art, and it is an object of the present invention to provide a method of resin sealing permanent magnets in a laminated rotor core, wherein filling operation of the resin material is immediately conducted without being affected by the preheating operation of the laminated core, and by which the operating efficiency of filling of the resin material is improved compared with conventional methods.